Search for γ -Ray Line Signals from Dark Matter Annihilations in the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

Abstract

Spectral lines are among the most powerful signatures for dark matter (DM) annihilation searches in very-high-energy γ rays. The central region of the Milky Way halo is one of the most promising targets given its large amount of DM and proximity to Earth. We report on a search for a monoenergetic spectral line from self-annihilations of DM particles in the energy range from 300 GeV to 70 TeV using a twodimensional maximum likelihood method taking advantage of both the spectral and spatial features of the signal versus background. The analysis makes use of Galactic center observations accumulated over ten years (2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) with the H.E.S.S. array of ground-based Cherenkov telescopes. No significant γ-ray excess above the background is found. We derive upper limits on the annihilation cross section hσvi for monoenergetic DM lines at the level of 4 × 10 −28 cm 3 s −1 at 1 TeV, assuming an Einasto DM profile for the Milky Way halo. For a DM mass of 1 TeV, they improve over the previous ones by a factor of 6. The present constraints are the strongest obtained so far for DM particles in the mass range 300 GeV-70 TeV. Groundbased γ-ray observations have reached sufficient sensitivity to explore relevant velocity-averaged cross sections for DM annihilation into two γ-ray photons at the level expected from the thermal relic density for TeV DM particles.

Precise yield of high-energy photons from Higgsino dark matter annihilation

“…Naively, one would expect that there should be no counterterm contributions as the tree-level contribution cancels. However, as also observed for the corresponding quarkonium calculation in QCD [40], 10 The matching coefficient for O 3 was previously given for j = 1 and Y = 0, i.e. the pure wino, in [20].…”

“…In this appendix, we collect the soft functions appearing in the factorization theorem for the intermediate resolution case (10) and discuss their resummation. We only give the non-vanishing soft-function coefficients.…”

“…Searches for this type of signature have already been performed by existing gammaray telescopes such as Fermi-LAT [9], H.E.S.S. [10] and MAGIC [11]. Particularly promising is the next-generation Cherenkov Telescope Array (CTA) [12], expected to improve the existing limits on spectral lines by one order of magnitude for TeV-scale gamma-ray energies.…”

“…The indices W, Y = 3, 4 appearing in the soft functions and the photon-jet function are adjoint indices of the SU(2)⊗U(1) Y group (indices W, Y = 4 denote the U(1) Y components). Specific expressions of these functions and their resummation are discussed in Appendix C. Relative to the wino case, a new component due to the hypercharge of the Higgsino appears in (10). There are three non-relativistic particle-pair indices I and J relevant for χ 0 1 χ 0 1 → γ+X annihilation.…”

Phenomenological consistency of the singlet-triplet scotogenic model

“…We also show the current bounds of the Fermi-LAT [64] collaboration for observation of the Milky Way halo in the low mass region ∼ (200 MeV−500 GeV) and the H.E.S.S. [65] bounds for the high mass region ∼ (300 GeV−70 TeV). After improving our scan as much as possible, we realize that all the points always fall under the Fermi-LAT bound in the low mass region.…”